The correct answer is A. because of desiccation and mechanical damage to the tissues.
Frost is a thin layer of ice that forms on surfaces when the temperature drops below freezing. When frost forms on plants, it can cause desiccation, or drying out, of the plant’s tissues. This is because frost crystals form on the surface of the plant and absorb water from the plant’s cells. The water loss can cause the plant’s cells to collapse and die.
Frost can also cause mechanical damage to plant tissues. When frost crystals form on the surface of the plant, they can expand and rupture the plant’s cells. This can cause the plant to wilt and die.
Respiration and transpiration are not the main causes of plant death from frost. Respiration is the process by which plants use oxygen to break down glucose and release energy. Transpiration is the process by which plants lose water vapor through their leaves. Both respiration and transpiration can slow down or stop at low temperatures, but they are not the main causes of plant death from frost.
In conclusion, plants are killed in winter by frost because of desiccation and mechanical damage to the tissues.